1. Field of the Invention
The present invention relates to a method and apparatus for recovering silver from spent photographic bleach-fix solutions containing iron, and concurrently regenerating the bleachfix. It relates more specifically to such a technique which utilizes an electrolytic cell to plate out and recover silver.
2. Prior Art
Electrolytic techniques for the recovery of silver from spent photographic solutions are well known, eg. as described in U.S. Pat. No. 1,629,212 to Giffer for treating a spent "hypo" fix.
The efficiencies of prior electrolytic systems were satisfactory for the recovery of silver from the thiosulfate fix solution (or "hypo") of the aforementioned patent. However, when the same techniques were applied to spent bleach-fix solutions containing soluble ferric iron ions, for example, such soluble iron complexes as ferric EDTA (ethylenediaminetetraacetic acid), the efficiency at acceptably low current densities was found to be much too low to be practical. We have concluded that such reduced efficiency is mainly due to the consumption of electrons by a competing cathode reaction whereby iron III is reduced to iron II before the silver is reduced. Concurrently there is a reoxidation of iron II back to iron III at the anode. Thus, current densities several times as great as normally required in silver recovery cells are required to obtain the same yields of silver.